Just how "autonomous" is an autonomous underwater vehicle (AUV) really? In the case of Spray, a sleek, torpedo-like glider designed by Scripps Institution of Oceanography (SIO) and WHOI engineers, pretty darn so.

In 2004, the bright red glider earned accolades for becoming the first robot to successfully traverse the raging Gulf Stream. Launched from southern Massachusetts in September, Spray reached Bermuda in less than two months, puttering along at an average speed of 12 miles a day. The whole time, it was busily collecting troves of oceanographic data that it would transmit back to its human masters at WHOI and Scripps.

One day, oceanographers hope Spray and other gliders will be able to roam the oceans at will, providing an almost limitless supply of data that could be used to build more sophisticated climate models and develop better weather forecasts.

If you've ever perused one of the deep-sea critter galleries featured on this site, you probably owe ROVs your deep and abiding gratitude. To capture this gorgeous jelly, photographers traveled to the Celebes Sea, the location of one of the world's deepest basins.

With the assistance of Global Explorer, a ROV equipped with a high definition color video camera and digital still camera, the researchers were able to snap some of the first pictures of numerous species that are believed to be new to science, including this red medusa jellyfish, which belongs to the genus Atolla. The critter's bright red coloration serves an unusual purpose: It masks the bioluminescence given off by any glowing prey that the jelly is in the process of digesting.

In a depth-defying feat of dazzling daring last year, the robot known as Nereus dove to the deepest spot in the ocean and spent 10 hours exploring a spot that is deeper than Mount Everest is high.

The record-setting Nereus collected samples from the seafloor with the help of a hefty manipulator arm (as seen in the image). Engineers at WHOI built Nereus to endure the deep sea's intense pressures, which effectively load each square inch of its surface with roughly 15,000 pounds--the same level of pressure you were to feel if someone placed three Hummers on your big toe.

On May 31, 2009, Nereus proved its seafaring mettle and plunged to a depth of 6.8 miles in the Pacific Ocean's Mariana Trench. Robots like Nereus will make it much easier for scientists to explore vast regions of the deep ocean that were once off-limits.

OK, so he's not an autonomous bot, but we simply have to give more props to the Deep Submergence Vehicle known as Alvin. The oldest and most venerable vehicle of its kind, Alvin has completed over 4,400 dives over the course of its momentous, 46-year career.

In the late 1970s, Alvin and his passengers discovered the first known hydrothermal vents, or "black smokers" as they are sometimes called. Initially, scientists thought that no species, let alone a bustling community, could survive the scorching temperatures and crushing pressures of these sites, most of which are located about 7,000 feet below the ocean surface in areas of seafloor spreading.

To their great surprise, researchers found out that not only did the magma-heated, mineral-rich water spurts support life, they nursed entire ecosystems.

Scientists were surprised that hydrothermal vents could harbor such a dizzying array of species. The real stunner, however, came in the form of what looked like a feathery, elongated lipstick tube: Riftia pachyptila, more commonly known as the giant tube worm.

Its discovery upended one of biology's core tenets: That all life essentially depends on the energy of the sun, either by using sunlight for photosynthesis or by munching photosynthesizing organisms. By contrast, in the tube worm millions of symbiotic bacteria that dwell within the its large plumes grab hydrogen sulfide and other noxious chemicals that seep from the vents and convert them into food and energy for their host, a process called chemosynthesis.

In 1998, a bot known as ROPOS ("Remotely Operated Platform for Ocean Science") sawed a black smoker free from the sea floor and hauled it up to allow scientists to examine its structure and unique organisms.

This pale, slithering creatures may look like something out of a sci-fi flick, but it is in fact a fish--a snailfish (Pseudoliparis amblystomopsis), to be precise. Amazing video footage of the snailfish, the first of a school of fish living in the deepest sea, was taken by the Hadal-Lander, a ROV with a titanium-encased high-resolution camera, in the Pacific's Japan Trench. These snailfish live almost five miles beneath the ocean surface, in pitch-black waters and under immense pressure.

To lure the elusive snailfish out into the open, the researchers strapped a dead mackerel to the lander; an energetic school of snailfish quickly located the appetizing carcass and made short work of it. The specimen seen above was recovered from a trap laid near the bait.

The researchers pronounced themselves shocked by the snailfish's vitality and sociability. "We thought the deepest fishes would be motionless, solitary, fragile individuals eking out an existence in a food-sparse environment," said researcher Monty Priede.